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Abstract:

There is provided an image sensor according to an aspect of the present
invention that includes: a reference image luminance extractor
partitioning a reference image into a plurality of reference image blocks
and extracting luminance values of edge pixels at the edges of each of
the plurality of reference image blocks to calculate a luminance weight
value for each of the edge pixels; a luminance weight value calculator
calculating a luminance weight value of each pixel of the corresponding
reference image block on the basis of luminance weight values of edge
pixels of the corresponding reference image block with respect to each of
the plurality of reference image blocks; and a luminance corrector
correcting the luminance of an input image by multiplying the luminance
weight value for each pixel calculated by the luminance weight value
calculator with respect to a luminance value of each pixel of the input
image.

Claims:

1. An image sensor, comprising: a reference image luminance extractor,
operative to partition a reference image into a plurality of reference
image blocks, extract luminance values of four edge pixels of each of the
plurality of reference image blocks and calculate a luminance weight
value for each of the edge pixels; a luminance weight value calculator
operatively coupled to the reference image luminance extractor, operative
to calculate a luminance weight value of each pixel of a corresponding
reference image block, on the basis of luminance weight values of four
edge pixels of the corresponding reference image block, for each of the
plurality of reference image blocks; and a luminance corrector
operatively coupled to the luminance weight value calculator, operative
to correct the luminance of an input image by multiplying the luminance
weight value for each pixel, calculated by the luminance weight value
calculator, with a luminance value of each pixel of the input image.

2. The image sensor of claim 1, wherein the reference image luminance
extractor is operative to calculate the luminance weight value on the
basis of the brightest luminance value among luminance values of all the
edge pixels extracted from the reference image.

3. The image sensor of claim 1, wherein the luminance weight value
calculator is operative to calculate the luminance weight values of each
pixel of the corresponding reference image block, in proportion to a
distance between each pixel and the four edge pixels of the corresponding
reference block for each of the plurality of reference image blocks.

4. The image sensor of claim 1, wherein the luminance corrector is
operative to clamp a corrected pixel value to a predetermined set minimum
value when the corrected pixel value is smaller than the predetermined
set minimum value.

5. The image sensor of claim 1, wherein the luminance corrector is
operative to clamp a corrected pixel value to a predetermined set maximum
value when the corrected pixel value is larger than the predetermined set
maximum value.

6. A method for correcting lens shading of an image sensor, comprising:
partitioning a reference image into a plurality of reference image blocks
and extracting luminance values of four edge pixels at the edges of each
of the plurality of reference image blocks and calculating a luminance
weight value for each of the edge pixels; calculating a luminance weight
value of each pixel of a corresponding reference image block, on the
basis of luminance weight values of four edge pixels of the corresponding
reference image block, for each of the plurality of reference image
blocks; and correcting the luminance of an input image by multiplying the
luminance weight value for each pixel, calculated by the luminance weight
value calculator, with a luminance value of each pixel of the input
image.

7. The method of claim 6, wherein calculating the luminance weight value
for each of the edge pixels, comprises: calculating the luminance weight
value on the basis of the brightest luminance value among luminance
values of all the edge pixels extracted from the reference image.

8. The method of claim 6, wherein calculating the luminance weight value
of each pixel of the corresponding reference image block, comprises:
calculating the luminance weight value in proportion to a distance
between each pixel and the four edge pixels of the corresponding
reference block for each of the plurality of reference image blocks.

9. The method of claim 6, wherein correcting the luminance, comprises:
clamping a corrected pixel value to a predetermined set minimum value
when the corrected pixel value is smaller than the predetermined set
minimum value.

10. The method of claim 6, wherein correcting the luminance, comprises:
clamping a corrected pixel value to a predetermined maximum value when
the corrected pixel value is larger than the predetermined set maximum
value.

11. An image sensor, comprising: a reference image luminance extractor,
operative to partition a reference image into a plurality of reference
image blocks, extract luminance values of four edge pixels at the edges
of each of the plurality of reference image blocks, and calculate a
luminance weight value for each of a plurality of edge pixels; a
luminance weight value difference storage, operatively coupled to the
reference image luminance extractor, operative to store a luminance
weight value difference between a luminance weight value of an edge pixel
and a luminance weight value of an adjacent edge pixel, adjacent to the
edge pixel, for each of the plurality of edge pixels; a luminance weight
value restorer, operatively coupled to the luminance weight value
difference storage, operative to restore the luminance weight value
difference to the luminance weight value; a luminance weight value
calculator, operatively coupled to the luminance weight value restorer,
operative to calculate a luminance weight value of each pixel of a
corresponding reference image block on the basis of luminance weight
values of four edge pixels of the corresponding reference image block for
the plurality of reference image blocks by using the luminance weight
value restored in the luminance weight value restorer; and a luminance
corrector, operatively coupled to the luminance weight value calculator,
operative to correct the luminance of an input image by multiplying a
luminance weight value for each pixel, calculated in the luminance weight
value calculator, by a luminance value of each pixel of the input image.

12. The image sensor of claim 11, wherein the size of data representing
the luminance weight value difference is smaller than the size of data
representing the luminance weight value.

13. The image sensor of claim 11, wherein the luminance weight value
difference storage is operative to calculate and store the luminance
weight value difference in accordance with a predetermined set order from
a reference edge pixel to another edge pixel by using any one pixel of
the plurality of edge pixels as the reference edge pixel.

14. The image sensor of claim 13, wherein the luminance weight value
difference storage is further operative to store a difference between the
luminance weight value of the edge pixel and a luminance weight value
just prior to the corresponding edge pixel in the predetermined set order
with respect to each of the plurality of edge pixels.

15. The image sensor of claim 11, wherein the reference image luminance
extractor is operative to calculate the luminance weight value on the
basis of the brightest luminance value among luminance values of all the
edge pixels extracted from the reference image.

16. The image sensor of claim 11, wherein the luminance weight value
calculator is operative to calculate the luminance weight values of four
edge pixels of the corresponding reference image block in proportion to a
distance between each pixel and four edge pixels with respect to each of
the plurality of reference image blocks.

17. The image sensor of claim 11, wherein the luminance corrector is
operative to clamp a corrected pixel value to a predetermined set minimum
value when the corrected pixel value is smaller than the predetermined
set minimum value.

18. The image sensor of claim 11, wherein the luminance corrector is
operative to clamp the corrected pixel value to a predetermined set
maximum value when the corrected pixel value is larger than the
predetermined set maximum value.

19. A method for correcting lens shading of an image sensor, comprising:
partitioning a reference image into a plurality of reference image
blocks, extracting luminance values of four edge pixels at the edges of
each of the plurality of reference image blocks and calculating a
luminance weight value for each of the edge pixels; storing a luminance
weight value difference between a luminance weight value of an edge pixel
and a luminance weight value of an adjacent edge pixel, adjacent to the
edge pixel, for each of the plurality of edge pixels; restoring the
luminance weight value difference to the luminance weight value;
calculating a luminance weight value of each pixel of a corresponding
reference image block on the basis of luminance weight values of four
edge pixels of the corresponding reference image block for the plurality
of reference image blocks by using the luminance weight value restored in
the luminance weight value restorer; and correcting the luminance of an
input image by multiplying a luminance weight value for each pixel,
calculated in the luminance weight value calculator, by a luminance value
of each pixel of the input image.

20. The method of claim 19, wherein the size of data representing the
luminance weight value difference is smaller than the size of data
representing the luminance weight value.

21. The method of claim 19, wherein storing the luminance weight value
difference, comprises: calculating and storing the luminance weight value
difference in accordance with a predetermined set order from a reference
edge pixel to another edge pixel by using any one pixel of the plurality
of edge pixels as the reference edge pixel.

22. The method of claim 20, wherein storing the luminance weight value
difference, comprises storing a difference between the luminance weight
value of the corresponding pixel and a luminance weight value just prior
to the corresponding edge pixel in the predetermined set order with
respect to each of the plurality of edge pixels.

23. The method of claim 19, wherein calculating the luminance weight
value for each of the edge pixels, comprises: calculating the luminance
weight value on the basis of the brightest luminance value among
luminance values of all the edge pixels extracted from the reference
image.

24. The method of claim 19, wherein calculating the luminance weight
value of each pixel of the corresponding reference image block,
comprises: calculating the luminance weight value in proportion to a
distance between each pixel and the four edge pixels of the corresponding
reference block for each of the plurality of reference image blocks.

25. The method of claim 19, wherein correcting the luminance, comprises:
clamping a corrected pixel value to a predetermined set minimum when the
corrected pixel value is smaller than the predetermined set minimum
value.

26. The method of claim 19, wherein correcting the luminance, comprises:
clamping a corrected pixel value to a predetermined maximum value when
the corrected pixel value is larger than the predetermined set maximum
value.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the priorities of Korean Patent Application
Nos. 10-2010-0059175 filed on Jun. 22, 2010 and 10-2010-0063071 filed on
Jun. 30, 2010, in the Korean Intellectual Property Office, the
disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a method and system for correcting
lens shading, and more particularly, to correcting lens shading of an
input image by acquiring a luminance weight value for an edge pixel in
each block by partitioning a photographed reference image into a
plurality of blocks.

[0004] 2. Description of the Related Art

[0005] In general, an image sensor is a device used for photographing an
image by using the properties of a semiconductor that reacts to light. An
image sensor is a device in which a pixel senses brightnesses and
wavelengths of different lights emitted from subjects, and converts the
sensed brightnesses and wavelengths into electrical values. Converting
the electrical value into a signal processable level is also the role of
the image sensor.

[0006] That is, the image sensor is a semiconductor element that converts
an optical image into an electrical signal. A charge coupled device (CCD)
is an element in which metal oxide semiconductor (MOS) capacitors are
positioned extremely close to one another, and electrical charges are
stored in and transferred to, the capacitors. A complementary metal oxide
semiconductor (CMOS) image sensor is an element that adopts a switching
type that sequentially detects an output by using a control signal and a
signal processing circuit as a peripheral circuit. The CMOS image sensor
is formed using MOS transistors in an amount equal to the number of
pixels.

[0007] The CMOS image sensor has a large advantage in that it has
low-power consumption, and therefore is very useful for personal portable
systems such as a cellular phone camera, PC camera and the like. The CMOS
image sensor can also be applied for various other purposes in addition
to those applicable to the consumer electronics field. For example, CMOS
image sensors may also be used in the medical field, the toy field, etc.,
and the like.

[0008] An image sensor generally photographs an optical image of a subject
through a lens. A problem is created by the lens in that a lens' shading
phenomenon causes change of luminance at an edge portion of a
photographed image compared to luminance at a center portion of an image.
This shading phenomenon is due to, for example, influence of the lens'
shape.

[0009] Therefore, the lens shading phenomenon should be corrected in order
to acquire a more true image. However, in the prior art, after a
luminance weight value is acquired for each of the entirety of the pixels
of the image sensor in order to correct the lens shading, a method of
multiplying a luminance weight value by each pixel of an input image is
used. Since the luminance weight value is calculated for all pixels and
stored, a memory having a large capacity is required.

SUMMARY OF THE INVENTION

[0010] An aspect of the present invention provides a method and system for
correcting lens shading of the image sensor capable of correcting a lens
shading phenomenon.

[0011] According to an aspect of the present invention, there is provided
an image sensor that includes: a reference image luminance extractor
partitioning a reference image into a plurality of reference image blocks
and extracting luminance values of edge pixels at the edges of each of
the plurality of reference image blocks to calculate a luminance weight
value for each of the edge pixels; a luminance weight value calculator
calculating a luminance weight value of each pixel of the corresponding
reference image block on the basis of luminance weight values of edge
pixels of the corresponding reference image block with respect to each of
the plurality of reference image blocks; and a luminance corrector
correcting the luminance of an input image by multiplying the luminance
weight value for each pixel calculated by the luminance weight value
calculator with respect to a luminance value of each pixel of the input
image.

[0012] According to another aspect of the present invention, there is
provided a method for correcting lens shading of an image sensor that
includes: partitioning a reference image into a plurality of reference
image blocks and extracting luminance values of edge pixels at the edges
of each of the plurality of reference image blocks to calculate a
luminance weight value for each of the edge pixels; calculating a
luminance weight value of each pixel of the corresponding reference image
block on the basis of luminance weight values of edge pixels of the
corresponding reference image block with respect to each of the plurality
of reference image blocks; and correcting the luminance of an input image
by multiplying the luminance weight value for each pixel calculated by
the luminance weight value calculator with respect to a luminance value
of each pixel of the input image.

[0013] According to an aspect of the present invention, there is provided
an image sensor that includes: a reference image luminance extractor
partitioning a reference image into a plurality of reference image blocks
and extracting luminance values of four edge pixels at the edges of each
of the plurality of reference image blocks to calculate luminance weight
values of a plurality of edge pixels; a weight value difference storage
storing a luminance weight value difference which is a difference between
a luminance weight value of the corresponding edge pixel for each of the
plurality of edge pixels and a luminance weight value of an edge pixel
adjacent to the corresponding edge pixel; a luminance weight value
restorer restoring the luminance weight value difference to the luminance
weight value; a luminance weight value calculator calculating a luminance
weight value of each pixel of the corresponding reference image block on
the basis of luminance weight values of four edge pixels of the
corresponding reference image block with respect to the plurality of
reference image blocks by using the luminance weight value restored in
the luminance weight value restorer; and a luminance corrector correcting
the luminance of an imputed image by multiplying a luminance weight value
for each pixel calculated in the luminance weight value calculator by a
luminance value of each pixel of the input image.

[0014] According to another aspect of the present invention, there is
provided a method for correcting lens shading of an image sensor that
includes: partitioning a reference image into a plurality of reference
image blocks and extracting luminance values of four edge pixels at the
edges of each of the plurality of reference image blocks to calculate
luminance weight values of a plurality of edge pixels; storing a
luminance weight value difference which is a difference between a
luminance weight value of the corresponding edge pixel for each of the
plurality of edge pixels and a luminance weight value of an edge pixel
adjacent to the corresponding edge pixel; restoring the luminance weight
value difference to the luminance weight value; calculating a luminance
weight value of each pixel of the corresponding reference image block on
the basis of luminance weight values of four edge pixels of the
corresponding reference image block with respect to the plurality of
reference image blocks by using the luminance weight value restored in
the luminance weight value restorer; and correcting the luminance of an
imputed image by multiplying a luminance weight value for each pixel
calculated in the luminance weight value calculator by a luminance value
of each pixel of the input image.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above and other aspects, features and other advantages of the
present invention will be more clearly understood from the following
detailed description taken in conjunction with the accompanying drawings,
in which:

[0016]FIG. 1 is a schematic block diagram of an image sensor according to
an exemplary embodiment of the present invention;

[0017] FIGS. 2A and 2B show an example of a reference image having a lens
shading phenomenon provided in a sensor unit of an image sensor;

[0019] FIGS. 4A and 4B are diagrams describing one example of calculating
a luminance weight value for one pixel of a reference image block
according to an exemplary embodiment of the present invention;

[0020]FIG. 5 is a flowchart illustrating a method for correcting lens
shading of an image sensor according to an exemplary embodiment of the
present invention;

[0021]FIG. 6 is a schematic block diagram of an image sensor according to
another exemplary embodiment of the present invention;

[0022]FIG. 7 is a schematic diagram for calculating a difference between
luminance weight values according to another exemplary embodiment of the
present invention; and

[0023]FIG. 8 is a flowchart illustrating a method for correcting lens
shading of an image sensor according to another exemplary embodiment of
the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0024] An image sensor according to an exemplary embodiment of the present
invention will now be described in detail with reference to the
accompanying drawings.

[0025]FIG. 1 is a schematic block diagram of an image sensor according to
an exemplary embodiment of the present invention. As shown in FIG. 1, the
image sensor 100 includes a luminance extractor 110, a luminance weight
value calculator 120 operatively coupled to the luminance extractor 110,
and a luminance corrector 130, operatively coupled to the luminance
weight value calculator 120.

[0026] The terminology "operatively coupled" as used herein refers to
coupling that enables operational and/or functional communication and
relationships there-between and may include any intervening items
necessary to enable such communication such as, for example, data
communication buses or any other necessary intervening items that one of
ordinary skill would understand to be present. Also, it is to be
understood that other intervening items may be present between
"operatively coupled" items even though such other intervening items are
not necessary to the functional communication facilitated by the
operative coupling. For example, a data communication bus may provide
data to several items along a pathway along which two or more items are
operatively coupled, etc.

[0027] The luminance extractor 110 is operative to partition a reference
image into a plurality of reference image blocks and to calculate a
luminance weight value by extracting luminance values of pixels at four
edges of each of the reference image blocks. For convenience, the pixels
at the four edges of each reference image block will be referred to as
"four edge pixels."

[0028] As shown in FIG. 1, the luminance extractor 110 may include a
reference image partitioning unit 111, operative to partition an input
reference image into a plurality of reference image blocks. The luminance
extractor 110 may further include an edge pixel luminance extracting unit
112, operatively coupled to the reference image partitioning unit 111.
The edge pixel luminance extracting unit 112 is operative to extract
luminance values of four edge pixels at each of the edges of a plurality
of partitioned reference image blocks. The luminance extractor 110 may
further include an edge pixel luminance weight value calculating unit
113, operatively coupled to the edge pixel luminance extracting unit 112.
The edge pixel luminance weight value calculating unit 113 is operative
to calculate a luminance weight value of an edge pixel on the basis of,
that is, based on, the luminance value extracted from the edge pixel.

[0029] The luminance extractor 110 and the various units, the luminance
weight value calculator 120 and the luminance corrector 130, may be
implemented in the various embodiments in various ways, such as, for
example, using hardwired logic, or using one or more processors. The one
or more processors may be, for example, a programmable processor having
software and/or firmware executing thereon, ASICs, DSPs, etc. Therefore,
the various embodiments may be implemented as hardwired logic, processors
or combinations thereof. An image sensor as disclosed herein may include
any processors, hardwired logic, etc., required to implement the various
embodiments as herein described.

[0030] The luminance weight value calculator 120 is operative to calculate
a luminance weight value of each pixel of the corresponding reference
image block on the basis of luminance weight values of four edge pixels
of the corresponding reference image block with respect to each of the
plurality of reference image blocks.

[0031] The luminance corrector 130 is operative to correct the luminance
of an input image by multiplying the luminance weight value for each
pixel calculated by the luminance weight value calculator 120 with
respect to a luminance value of each pixel of the input image.

[0032] The image sensor 100 configured as above operates as follows.

[0033] First, the image sensor 100 receives a reference image for
correcting lens shading from a sensor unit (not shown). The sensor unit
may generally include a color filter array, an analog/digital converter,
a lens section, and the like.

[0034] The color filter array converts an optical subject signal input
through the lens section into an electrical signal and outputs the
corresponding signal. The color filter array may adopt a bayer pattern
which is advantageous in terms of resolution. The analog/digital
converter converts the image signal converted by the color filter array
into a digital signal.

[0035] The reference image may be a single-color image and, for example,
may be a white image acquired by photographing a white chart. When the
reference image is input through the sensor unit, the luminance of the
reference image is not uniform due to the lens shading phenomenon. Such
an example is shown in FIG. 2. FIGS. 2A and 2B show an example of a
reference image having a lens shading phenomenon provided in a sensor
unit of an image sensor. FIG. 2A illustrates a reference image of which
luminance decreases toward an edge from the center and FIG. 2B
illustrates a reference image in which luminance is high at a plurality
of points and luminance decreases as it is further from the points. The
lens shading phenomenon may occur due to a lens' own characteristic or
nonuniformity generated while manufacturing the lens section.

[0037] For example, the reference image may be partitioned into
17×13 reference image blocks and in the exemplary embodiment, each
block may have a pixel array of 160×160. Therefore, the number of
reference image blocks may be variable by the entire pixel array size of
the reference image and the pixel array of each block.

[0038] Next, the edge pixel luminance extracting unit 112 of the reference
image luminance extractor 110 extracts a luminance value of each edge
pixel from the partitioned reference image blocks. Since each reference
image block has four edges, for example, when the reference image is
partitioned into 17×13 reference image blocks, luminance values for
a total of 18×14 (=252) edges are extracted.

[0039] When all of the luminance values of the edge pixels are extracted,
the edge pixel luminance weight value calculating unit 113 of the
reference image luminance extractor 110 calculates a luminance weight
value for each edge pixel on the basis of all the extracted luminance
values. The luminance weight value as a value (gain) multiplied by the
pixel value of the input image in order to correct the lens shading
phenomenon is set as a large value for a pixel having a dark luminance
value by lens shading and in contrast, as a small value for a pixel
having a bright luminance value. For example, in the exemplary
embodiment, the luminance weight value may be calculated on the basis of
the brightest luminance value among the extracted luminance values of all
edge pixels in the reference image. That is, the luminance weight value
is set as 1 for the pixel having the brightest luminance value and may be
set as a value larger than 1 depending on a ratio to the brightest
luminance value for a pixel having a luminance value smaller than the
brightest luminance value.

[0040] The acquired luminance weight value for each edge pixel is stored
in a memory such as, for example, SRAM. Accordingly, according to the
exemplary embodiment of the present invention, since the weight value is
just calculated at only edges in the partitioned reference image blocks
without calculating all the weight values for the entirety of the pixels
of the reference image, the luminance weight value may be very rapidly
calculated and in addition, since the number of luminance weight values
is much smaller than that in the case of acquiring the luminance weight
values for all the pixels, it is possible to reduce even the capacity of
the memory storing the luminance weight value.

[0041] The luminance weight value for each edge pixel is preferably
calculated for each of Gr, Gb, R, and B constituting the Bayer pattern.
Hereinafter, it should be noted that the term "pixel" as used herein may
include four individual components that may also be referred to as pixels
(and which may also be considered "subpixels") of Gr, Gb, R, and B
constituting the bayer pattern. That is, some embodiments may calculate
luminance weight values for some, or all, subpixels of the Bayer pattern
corresponding to each pixel.

[0042] Next, the luminance weight value calculator 120 calculates
luminance weight values for all pixels of the corresponding block on the
basis of the pixel weight values of four edge pixels of the corresponding
block in each reference image block. In the exemplary embodiment, the
luminance weight value calculator 120 calculates the luminance weight
value of each pixel of the corresponding reference image block in
proportion to distances between each pixel and four edge pixels with
respect to each reference image block.

[0043] FIGS. 4A and 4B are a diagram describing one example of calculating
a luminance weight value for one pixel of a reference image block. In
particular, FIG. 4A describes a first step of calculating a luminance
weight value and FIG. 4B is a diagram describing a second step of
calculating a luminance weight value.

[0044] As shown in FIG. 4A, at the first step of calculating the luminance
weight value, two pixels Pi1 and Pim which are in the same row
as edge pixels P11, P1n, Pm1, and Pmn, among pixels
which are in the same column as a pixel Pij of which a luminance
weight value is calculated are determined and luminance weight values of
the determined pixels are calculated in proportion to distances by using
distances x and y from luminance weight values of edge pixels P11
and P1n for an edge pixel which is in the same row as the determined
pixels, that is, a pixel Pil and luminance weight values of edge
pixels Pm1 and Pmn, for a pixel Pin.

[0045] Next, as shown in FIG. 4B, at the second step of calculating the
luminance weight value, the luminance weight value of two pixels Pi1
and Pin, are calculated in proportion to a distance in accordance
with distances x' and y' between two pixels Pi1 and Pin,
acquired at the first step and the corresponding pixel Pij so as to
acquire a luminance weight value of the corresponding pixel Pij.

[0046] Such a process is performed with respect to all the pixels of the
reference image block and in addition, such a process is performed even
with respect to all the reference image blocks so as to calculate the
luminance weight values of all the pixels. Further, the weight
calculation method is just one example and another calculation method may
also be applied.

[0047] The luminance corrector 130 receives an input image and multiplies
the luminance weight value corresponding to the pixel calculated in the
weight value calculator 120 by the corresponding luminance value for each
pixel of the input image. At this time, when the luminance value of each
pixel of the input image is corrected, the luminance weight value
calculator 120 calculates the luminance weight value of the corresponding
pixel and provides the calculated luminance weight value to the luminance
corrector 130 in an on-the-fly scheme. Accordingly, the luminance weight
value for each pixel does not need to be additionally stored.

[0048] In the exemplary embodiment of the present invention, when a
corrected pixel value of the pixel of the input image, that is, a pixel
value acquired by multiplying a luminance weight value of an original
pixel value by the original pixel value is smaller than a predetermined
set minimum value, the luminance corrector 130 preferably clamps the
pixel value to a minimum value. For example, the minimum value may be 0.
Further, when the corrected pixel value of the input image is larger than
a predetermined set maximum value, the luminance corrector 130 preferably
clamps the pixel value to the maximum value. For example, when the number
of bits representing the pixel value is n, the maximum value may be
2n. Since the pixel value is a digital value, when the pixel value
deviates from a range of a value which can be provided in terms of a
characteristic of the digital value, a luminance value of an image
actually displayed on a screen may be inverted. Therefore, it is possible
to improve the quality of an output image by clamping the pixel value
which deviates from the range to the maximum value or the minimum value.

[0049] Through such a process, a correction may be made for lens shading
for the input images, and the corrected images may be output.

[0050] Next, referring to FIG. 5, a method for correcting lens shading of
an image sensor according to an exemplary embodiment of the present
invention will be described.

[0051]FIG. 5 is a flowchart illustrating a method for correcting lens
shading of an image sensor according to an exemplary embodiment of the
present invention. As shown in FIG. 5, the method for correcting lens
shading of an image sensor according to the exemplary embodiment of the
present invention includes extracting the luminance of a reference image
(S110), calculating a luminance weight value (S120), correcting luminance
(S130), clamping to a minimum value (S140 and S150), and clamping to a
maximum value (S160 and S170).

[0052] At the extracting of the luminance of the reference image (S110), a
reference image is partitioned into a plurality of reference image blocks
and luminance values of four edge pixels in each of the plurality of
reference image blocks are extracted so as to calculate the luminance
weight value. At this time, the luminance weight value may be calculated
on the basis of the brightest luminance value among the luminance values
of all edge pixels extracted in the reference image.

[0053] At the calculating of the luminance weight value (S120), a
luminance weight value of each pixel of the corresponding reference image
block is calculated on the basis of luminance weight values of four edge
pixels of the corresponding reference image with respect to each of the
plurality of reference image blocks. At this time, the luminance weight
values of four edge pixels of the corresponding reference image block may
be calculated in proportion to a distance between each pixel and four
edge pixels with respect to each of the plurality of reference image
blocks.

[0054] During the correcting of the luminance (S130), by multiplying a
luminance value of each pixel of an input image by a luminance weight
value for each pixel calculated in a luminance weight value calculator,
the luminance of the input image is corrected. Thereafter, a corrected
pixel value of the pixel of the input image is compared with a
predetermined set minimum value (S140) and when the corrected pixel value
of the pixel of the input image is smaller than the predetermined set
minimum value (S140-YES), the corresponding pixel value is clamped to the
minimum value (S150). Further, the corrected pixel value of the pixel of
the input image is compared with a predetermined set maximum value (S160)
and when the corrected pixel value of the pixel of the input image is
smaller than the predetermined set minimum value (S160-YES), the
corresponding pixel value is clamped to the minimum value (S170).

[0055] A detailed description of the flow diagram illustrated in FIG. 5
corresponds to an operation of the image sensor according to the
exemplary embodiment of the present invention described with reference to
FIGS. 1 to 4, discussed in detail above.

[0056] As such, according to the exemplary embodiment, instead of
previously calculating and storing the luminance weight values of all the
pixels with respect to the reference image in a memory, the luminance
weight values of four edge pixels for each of the partitioned reference
image blocks are calculated and the luminance weight values of all the
pixels are calculated by using the calculated luminance weight value at
the time of correcting the luminance of the input image so as to markedly
reduce the size of a memory for storing the luminance weight value for
correcting the lens shading.

[0057] Further, according to the exemplary embodiment, since the luminance
weight value of each pixel is calculated on the basis of the luminance
weight value of each edge pixel by partitioning the reference image into
the plurality of reference image blocks, the input image may be corrected
in the case in which the lens shading phenomenon causes the problems
illustrated in FIG. 2A and FIG. 2B. For example, the embodiments provide
image correction where luminance decreases toward the edge from the
center as shown in FIG. 2A, and also provide image correction in the case
where luminance is high at a plurality of points while luminance
decreases as it is further away from the plurality of points as shown in
FIG. 2B.

[0058] Through such a process, a correction may be made for lens shading
for the input images, and the corrected images may be output.

[0059] Referring to FIG. 6, an image sensor according to another exemplary
embodiment of the present invention will be described.

[0060]FIG. 6 is a schematic block diagram of an image sensor 200
according to another exemplary embodiment of the present invention. As
shown in FIG. 6, the image sensor 200 includes a reference image
luminance extractor 210, a luminance weight value difference calculator
220 operatively coupled to the reference image luminance extractor 210, a
luminance weight value restorer 230 operatively coupled to the luminance
weight value difference calculator 220, a luminance weight value
calculator 240 operatively coupled to the luminance weight value restorer
230, and a luminance corrector 250 operatively coupled to the luminance
weight value calculator 240. The reference image luminance extractor 210,
luminance weight value difference calculator 220, luminance weight value
restorer 230, luminance weight value calculator 240, and luminance
corrector 250, may be implemented in the various embodiments in various
ways, such as, for example, using hard wired logic, or using one or more
processors. The one or more processors may be, for example, a
programmable processor having software and/or firmware executing thereon,
ASICs, DSPs, etc. Therefore, the various embodiments may be implemented
as hardwired logic, processors or combinations thereof. Further,
luminance weight value difference storage may be implemented as including
a separate memory, or an integrated memory integrated with, for example,
a processor as described above. That is, an image sensor as disclosed
herein with respect to FIG. 6 may include any processors, hardwired
logic, integrated or separate memory etc., required to implement the
various embodiments as herein described.

[0061] The reference image luminance extractor 210 is operative to
partition a reference image into a plurality of reference image blocks,
and calculate luminance weight values of a plurality of edge pixels by
extracting luminance values of four edge pixels at each of edges of the
plurality of reference image blocks. The luminance weight value
difference calculator 220 is operative to calculate a luminance weight
value difference, which is a difference between a luminance weight value
of an edge pixel for a given edge and a luminance weight value of a
corresponding edge pixel on an edge adjacent to the given edge, with
respect to each of the plurality of edge pixels. The calculated luminance
weight differences may then be stored in a memory such as, for example,
SRAM.

[0062] If the difference is between a given edge and a previous edge, it
may be noted that the first edge may not have a previous edge with which
to find a difference. In that case, the difference may be set to zero
while the actual luminance weight value may be stored in memory for
reference value. Alternatively, the memory that stores the difference
values may also store the luminance weight value for first edges. The
method of storing these difference values may be design dependent.

[0063] The luminance weight value restorer 230 is operative to restore the
luminance weight value difference to the luminance weight value. The
luminance weight value calculator 240 is operative to calculate a
luminance weight value of each pixel of the corresponding reference image
block on the basis of the luminance weight values of four edge pixels of
the corresponding reference image block with respect to the plurality of
reference image blocks. The luminance corrector 250 is operative to
correct the luminance of the input image by multiplying the luminance
weight value for each pixel calculated by the luminance weight value
calculator 240 with respect to a luminance value of each pixel of the
input image.

[0064] The image sensor 200 configured as above operates as follows.

[0065] First, the image sensor 200 receives a reference image for
correcting lens shading from a sensor unit (not shown). As described
above regarding the image sensor 100, a sensor unit of the image sensor
200 may generally include a color filter array, an analog/digital
converter, a lens section, and the like.

[0066] Next, the reference image luminance extractor 210 partitions the
input reference image into the plurality of reference image blocks. The
method utilized for partitioning the reference image may be the same as
the exemplary method described with reference to FIG. 3.

[0067] When all the luminance values for each edge pixel are extracted,
the luminance weight value for each edge pixel is calculated on the basis
of the extracted luminance values. The luminance weight value may be
calculated in the same manner as the method in which the reference image
luminance extractor 210 extracts the luminance.

[0068] When the luminance weight value is calculated, the reference image
luminance extractor 210 outputs the luminance weight value to the weight
value difference calculator 220. The weight value difference calculator
220 calculates a difference between the luminance weight value of the
corresponding edge pixel and the luminance weight value of an edge pixel
adjacent to the corresponding edge pixel with respect to each of the
plurality of edge pixels in the luminance weight value of each edge pixel
input from the reference image luminance extractor 210 and stores the
result as the luminance weight value difference.

[0069] For example, the luminance weight value difference calculator 220
uses any one pixel, of the plurality of edge pixels, as a reference edge
pixel, and calculates a luminance weight value difference in accordance
with a predetermined order from the reference edge pixel to another edge
pixel and may store the calculated luminance weight value difference as
the luminance weight value difference. At this time, the luminance weight
value difference calculator 220 may store a difference between the
luminance weight value of the corresponding edge pixel and a luminance
weight value of an edge pixel just prior to the corresponding edge pixel
in a predetermined order as the luminance weight value difference of the
corresponding edge pixel with respect to each of the plurality of edge
pixels.

[0070] In terms of the characteristic of the lens shading phenomenon, a
difference in luminance between two adjacent pixels in the reference
image is not large. For example, referring to FIG. 7 which is a schematic
diagram for calculating the luminance weight value difference according
to the exemplary embodiment of the present invention, the reference edge
pixel is E11 and luminance weight value differences between the reference
edge pixel E11 and edge pixels E12, E13, E14, . . .
arranged at the right side from the reference edge pixel E11 are
calculated. At this time, values displayed in parentheses of the edge
pixels (E11, E12, E13, and E14, . . . ) are luminance
weight values. Next, differences between the luminance weight values of
the edge pixels (E12, E13, and E14, . . . ) and luminance
weight values of adjacent edge pixels are calculated. That is, a
difference in pixel weight value between the edge pixel E12 and the
reference edge pixel E11, a difference in pixel weight value between
the edge pixel E13 and the edge pixel E12, and a difference in
pixel weight value between the edge pixel E14 and the reference edge
pixel E13 are calculated. The calculated values are -5, -7, and -6
which are values shown below the edge pixels. As known in FIG. 3, the
luminance weight value difference is smaller than the luminance weight
value of each edge pixel. It is to be understood that in the above
description, the magnitudes of the luminance weight value and the
luminance weight value difference are provided as exemplary and that
various different magnitudes, for example, values such as 1, 1.1, 1.2,
and the like may be used in accordance with the embodiments.

[0071] Therefore, the size of data representing the luminance weight value
difference may be smaller than the size of data representing the
luminance weight value, thereby markedly reducing the size of a memory
for storing the luminance weight value.

[0072] Accordingly, according to the exemplary embodiment of the present
invention, since the weight value is just calculated at only edges in the
partitioned reference image blocks, without calculating the entirety of
the weight values for the pixels of the reference image, the luminance
weight value may be very rapidly calculated. In addition, since the
number of luminance weight values is much smaller than that in the case
of acquiring the luminance weight values for all the pixels, and because
the luminance weight value is not stored but processed to the luminance
weight value difference (which has a smaller magnitude than the luminance
weight value) and stored, it is possible to reduce the memory capacity
required to store the luminance data (i.e the luminance weight value
difference is stored instead of the luminance weight values).

[0073] The luminance weight value for each edge pixel is preferably
calculated for each of Gr, Gb, R, and B constituting the Bayer pattern.
As previously discussed above, the term "pixel" as used herein may
include the four Bayer pattern components of Gr, Gb, R, and B. In
addition, as described above, the reference image luminance extractor 210
calculates the luminance weight values of all the edge pixels and
thereafter, the luminance weight value difference calculator 220
calculates and stores the luminance weight value difference.

[0074] However, the invention need not be so limited. Various embodiments
of the invention may calculate luminance weight value differences ranging
from differences for one pixel from each edge to all pixels from each
edge. Similarly, various embodiments of the invention may also form
groups of adjacent pixels at an edge of each reference image block and
calculate luminance weight value differences between the groups for 2
sequential edges. Therefore, when using groups of pixels, various
embodiments of the invention may define a size of groups as being one or
more pixel. Additionally, the number of groups used may also vary. The
specific number of pixels used in a group and the number of groups used
may be design and/or implementation dependent.

[0075] The stored luminance weight value difference is restored to the
luminance weight value for correcting lens shading for an input image in
the restorer 230. For example, the luminance weight value of the
reference edge pixel is added to a luminance weight value difference for
a subsequent edge pixel to calculate a luminance weight value of the
subsequent edge pixel and in the same method, a luminance weight value
for another subsequent edge pixel is calculated on the basis of the
calculated luminance weight value. When such a process is completed, the
luminance weight values of all the edge pixels are calculated.

[0076] When the luminance weight value of each edge pixel is calculated,
the luminance weight value calculator 240 calculates luminance weight
values for all pixels of the corresponding block on the basis of the
pixel weight values of four edge pixels of the corresponding block in
each reference image block. In the exemplary embodiment, the luminance
weight value calculator 240 calculates the luminance weight value of each
pixel of the corresponding reference image block in proportion to
distances between each pixel and four edge pixels with respect to each
reference image block.

[0077] The luminance weight value of one pixel of the reference image
block may be calculated in the same method as the method described with
reference to FIGS. 4A and 4B. Such a process is performed for all pixels
of the reference image block and in addition, such a process is performed
even with respect to all the reference image blocks so as to calculate
luminance weight value of all the pixels. Further, the weight calculation
method is just one example, and another calculation method may also be
applied.

[0078] The luminance corrector 250 receives an input image and multiplies
the luminance weight value corresponding to the pixel calculated in the
weight value calculator 240 by the corresponding luminance value for each
pixel of the input image. At this time, when the luminance value of each
pixel of the input image is corrected, the luminance weight value
calculator 240 calculates the luminance weight value of the corresponding
pixel and provides the calculated luminance weight value to the luminance
corrector 250 in an on-the-fly scheme. Accordingly, the luminance weight
value for each pixel does not need to be additionally stored.

[0079] In the exemplary embodiment of the present invention, when a
corrected pixel value of the pixel of the input image, that is, a pixel
value acquired by multiplying a luminance weight value of an original
pixel value by the original pixel value is smaller than a predetermined
set minimum value, the luminance corrector 250 preferably clamps the
pixel value to a minimum value. For example, the minimum value may be 0.
Further, when the corrected pixel value of the input image is larger than
a predetermined set maximum value, the luminance corrector 250 preferably
clamps the pixel value to the maximum value. For example, when the number
of bits representing the pixel value is n, the maximum value may be
2n. Since the pixel value is a digital value, when the pixel value
deviates from a range of a value which can be provided in terms of a
characteristic of the digital value, a luminance value of an image
actually displayed on a screen may be inverted. Therefore, it is possible
to improve the quality of an output image by clamping the pixel value
which deviates from the range to the maximum value or the minimum value.

[0080] Through such a process, a correction may be made for lens shading
for the input images, and the corrected images may be output.

[0081] Next, referring to FIG. 8, a method for correcting lens shading of
an image sensor according to another exemplary embodiment of the present
invention will be described.

[0082]FIG. 8 is a flowchart illustrating a method for correcting lens
shading of an image sensor according to another exemplary embodiment of
the present invention. As shown in FIG. 8, the method for correcting lens
shading of an image sensor according to an exemplary embodiment of the
present invention includes extracting the luminance of a reference image
(S210), storing a luminance weight value difference (S220), restoring a
luminance weight value (S230), calculating the luminance weight value
(S240), correcting luminance (S250), clamping to a minimum value (S260
and S270), and clamping to a maximum value (S280 and S290).

[0083] At the extracting of the luminance of the reference image (S110), a
reference image is partitioned into a plurality of reference image blocks
and luminance values of four edge pixels in each of the plurality of
reference image blocks are extracted so as to calculate luminance weight
values of a plurality of edge pixels. At this time, the luminance weight
value may be calculated on the basis of the brightest luminance value
among the luminance values of all edge pixels extracted in the reference
image.

[0084] During the storing of the luminance weight value difference (S220),
the luminance weight value difference which is a difference between a
luminance weight value of the corresponding edge pixel and a luminance
weight value of an edge pixel adjacent to the corresponding edge pixel is
stored with respect to each of the plurality of edge pixels. At this
time, any one pixel of the plurality of edge pixels is used as a
reference edge pixel and a luminance weight value difference may be
calculated and stored in accordance with a predetermined order from the
reference edge pixel to another edge pixel. Further, a difference between
the luminance weight value of the corresponding edge pixel and a
luminance weight value of an edge pixel just prior to the corresponding
edge pixel in a predetermined order may be stored as the luminance weight
value difference of the corresponding edge pixel with respect to the
plurality of edge pixels.

[0085] During the restoring of the luminance weight value (S230), the
luminance weight value is restored to the luminance weight value
difference.

[0086] During the calculating of the luminance weight value (S240), a
luminance weight value of each pixel of the corresponding reference image
block is calculated on the basis of luminance weight values of four edge
pixels of the corresponding reference image block with respect to each of
the plurality of reference image blocks by using the luminance weight
value restored at the restoring of the luminance weight value (S130). At
this time, the luminance weight values of four edge pixels of the
corresponding reference image block may be calculated in proportion to a
distance between each pixel and four edge pixels with respect to each of
the plurality of reference image blocks.

[0087] During the correcting of the luminance (S250), by multiplying a
luminance value of each pixel of an input image by a luminance weight
value for each pixel calculated in a luminance weight value calculator,
the luminance of the input image is corrected. Thereafter, a corrected
pixel value of the pixel of the input image is compared with a
predetermined set minimum value (S260) and when the corrected pixel value
of the pixel of the input image is smaller than the predetermined set
minimum value (S260-YES), the corresponding pixel value is clamped to the
minimum value (S270). Further, the corrected pixel value of the pixel of
the input image is compared with a predetermined set maximum value (S280)
and when the corrected pixel value of the pixel of the input image is
smaller than the predetermined set minimum value (S280-YES), the
corresponding pixel value is clamped to the minimum value (S290).

[0088] A detailed description of each step illustrated in FIG. 8
corresponds to an operation of the image sensor according to the
exemplary embodiment of the present invention described with reference to
FIGS. 6 to 8, discussed in detail above.

[0089] As such, according to an apparatus and a method for correcting lens
shading of the image sensor according to the exemplary embodiments of the
present invention described herein, instead of previously calculating and
storing the luminance weight values of all the pixels with respect to the
reference image in a memory, the luminance weight values of four edge
pixels for each of the partitioned reference image blocks are calculated
and the luminance weight values of all the pixels are calculated by using
the calculated luminance weight value at the time of correcting the
luminance of the input image so as to reduce the size of a memory for
storing the luminance weight value for correcting the lens shading.

[0090] Further, according to all of the various exemplary embodiments
described above, since the luminance weight value of each pixel is
calculated on the basis of the luminance weight value of each edge pixel
by partitioning the reference image into the plurality of reference image
blocks, the input image may be corrected in the case in which the lens
shading phenomenon causes the problems illustrated in FIG. 2A and FIG.
2B. For example, the embodiments provide image correction where luminance
decreases toward the edge from the center as shown in FIG. 2A, and also
provide image correction in the case where luminance is high at a
plurality of points and the luminance decreases as it is further from the
plurality of points as shown in FIG. 2B.

[0091] Through such a process, the input image of which lens shading
correction is completed among the input image is output as was discussed
for each of the embodiments described above.

[0092] As set forth above, according to exemplary embodiments of the
invention, there is provided a method and system capable of correcting
lens shading.

[0093] While the present invention has been shown and described in
connection with the exemplary embodiments, it will be apparent to those
skilled in the art that modifications and variations can be made without
departing from the spirit and scope of the invention as defined by the
appended claims.